Print first n entries

storage_engine/src/binary_coding.rs

@@ -0,0 +1,78 @@
+use bincode;
+use bincode::{Decode, Encode};
+use bincode::config::{BigEndian, Configuration, Fixint};
+use std::mem::size_of;
+
+const BIN_CONFIG: Configuration<BigEndian, Fixint> = bincode::config::standard().with_big_endian().with_fixed_int_encoding();
+
+pub fn encode<T: Encode>(t: &T) -> Result<Vec<u8>, bincode::error::EncodeError> {
+    bincode::encode_to_vec(t, BIN_CONFIG)
+}
+
+pub fn decode<T: Decode>(bytes: &[u8]) -> Result<(T, usize), bincode::error::DecodeError> {
+    bincode::decode_from_slice(bytes, BIN_CONFIG)
+}
+
+pub fn encode_vector<T: Encode>(ts: &[T]) -> Result<Vec<u8>, bincode::error::EncodeError> {
+    let size: usize = ts.len();
+    let mut result = encode(&size)?;
+    for t in ts {
+        result.append(&mut encode(&t)?);
+    }
+    Ok(result)
+}
+
+pub fn decode_vector<T: Decode>(bytes: &[u8]) -> Result<Vec<T>, bincode::error::DecodeError> {
+    let mut offset = size_of::<usize>();
+    let result_len: usize = decode(&bytes[..offset])?.0;
+    let mut result: Vec<T> = Vec::with_capacity(result_len);
+    for _ in 0..result_len {
+        let (x, bytes_consumed) = decode::<T>(&bytes[offset..])?;
+        offset += bytes_consumed;
+        result.push(x);
+    }
+    Ok(result)
+}
+
+// We don't care about encoding the length here (since it will be used for a row with known column
+// size)
+pub fn encode_sequence<T: Encode>(ts: &[T]) -> Result<Vec<u8>, bincode::error::EncodeError> {
+    let mut result = vec![];
+    for t in ts {
+        result.append(&mut encode(&t)?);
+
+    }
+    Ok(result)
+}
+
+pub fn decode_sequence<T: Decode>(len: usize, bytes: &[u8]) -> Result<Vec<T>, bincode::error::DecodeError> {
+    let mut result: Vec<T> = Vec::with_capacity(len);
+    let mut offset = 0;
+    for _ in 0..len {
+        let (x, bytes_consumed) = decode::<T>(&bytes[offset..])?;
+        offset += bytes_consumed;
+        result.push(x);
+    }
+    Ok(result)
+}
+
+
+fn example_encoding_decoding() {
+    let xs: Vec<u32> = vec![123, 250, 256, 123, 123, 123];
+    let xs: Vec<u32> = vec![];
+    let xs: Vec<u32> = vec![123];
+    let xs: Vec<u32> = vec![123, 250];
+
+    let xs: Vec<String> = vec!["foo".to_string(), "bar".to_string()];
+
+
+    println!("original {:?}", xs);
+    let exs = encode_vector(&xs[..]).unwrap();
+    println!("encoded {:?}", exs);
+
+    // WARNING: Don't forget to specify the type here
+    // let dxs = decode_vector::<u32>(&exs[..]).unwrap();
+    let dxs = decode_vector::<String>(&exs[..]).unwrap();
+    println!("decoded {:?}", dxs);
+}
+

storage_engine/src/error.rs

@@ -0,0 +1,44 @@
+#[derive(Debug)]
+pub enum Error {
+    DecodeError(DecodeErrorKind, bincode::error::DecodeError),
+    EncodeError(bincode::error::EncodeError),
+    IoError(std::io::Error),
+    InvalidStoreHeader,
+}
+
+#[derive(Debug)]
+pub enum DecodeErrorKind {
+    StoreHeaderNumberOfColumns,
+    StoreHeaderDeletedCount,
+    EntryData,
+    EntryIsDeleted,
+    EntryDataSize
+}
+
+// ===Errors===
+impl Error {
+    pub fn to_io_or_panic(self) -> std::io::Error {
+        use Error::*;
+        match self {
+            IoError(err) => err,
+            err => {
+                println!("{:?}", err);
+                panic!();
+            }
+        }
+    }
+}
+
+impl From<bincode::error::EncodeError> for Error {
+    fn from(err: bincode::error::EncodeError) -> Self {
+        Self::EncodeError(err)
+    }
+}
+
+impl From<std::io::Error> for Error {
+    fn from(err: std::io::Error) -> Self {
+        Self::IoError(err)
+    }
+}
+
+

storage_engine/src/lib.rs

@@ -1,2 +1,3 @@
-
 pub mod storage_engine;
+mod binary_coding;
+mod error;

storage_engine/src/main.rs

@@ -2,47 +2,85 @@ use tokio::sync::{Mutex, RwLock};
 use tokio::fs::{File, OpenOptions};
 use tokio::io::{BufReader, BufWriter, AsyncReadExt, AsyncWriteExt, AsyncSeekExt, SeekFrom};
 use tokio::fs;
+use std::path::Path;
 
 mod storage_engine;
+mod binary_coding;
+mod error;
 
 use crate::storage_engine::*;
 
+type Data = u32;
+
+const TABLE_PATH: &'static str = "test_table";
+
+type Result<T> = std::result::Result<T, std::io::Error>;
+
+async fn create_store() -> Result<Store<Data>> {
+    let mut store: Store<Data> = Store::new(TABLE_PATH, 5).await.map_err(|e| e.to_io_or_panic())?;
+    println!("CREATED");
+    println!("{:?}", store.read_all_bytes().await?);
+
+    let entry0: Entry<u32> = Entry::new_deleted(vec![1, 2, 3, 4, 5]);
+    append_entry(&mut store, &entry0).await?;
+
+    let entry1: Entry<u32> = Entry::new_deleted(vec![200, 200, 5, 6, 7]);
+    append_entry(&mut store, &entry1).await?;
+
+    println!("{:?}", store.read_all_bytes().await?);
+    Ok(store)
+}
+async fn connect_store() -> Result<Store<Data>> {
+    let mut store: Store<Data> = Store::connect(TABLE_PATH).await.map_err(|e| e.to_io_or_panic())?;
+    println!("CONNECTED");
+    println!("{:?}", store.read_all_bytes().await?);
+    Ok(store)
+}
+
+async fn create_or_connect() -> Result<Store<Data>> {
+    let exists = storage_engine::store_exists(TABLE_PATH).await.map_err(|e| e.to_io_or_panic())?;
+    if exists {
+        connect_store().await
+    } else {
+        create_store().await
+    }
+}
+
+
+async fn append_entry(store: &mut Store<Data>, entry: &Entry<Data>) -> Result<Cursor>{
+    println!("APPENDING");
+    println!("entry == {:?}", entry);
+    let cursor: Cursor = store.append_entry(&entry).await.map_err(|e| e.to_io_or_panic())?;
+    println!("cursor == {:?}", cursor);
+    Ok(cursor)
+}
+
+async fn read_entry(store: &mut Store<Data>, cursor: Cursor) -> Result<EntryDetailed<Data>>{
+    println!("READING ENTRY at cursor={}", cursor);
+    let entry = store.read_entry_at(cursor).await.map_err(|e| e.to_io_or_panic())?;
+    println!("ENTRY: {:?}", entry);
+    Ok(entry)
+}
+
+
 #[tokio::main]
-async fn main() -> Result<(), std::io::Error> {
+async fn main() -> Result<()> {
     println!("STOOOOOOOOOOOORAAAAAAAAAAAGE");
 
-    let blob_name = "blob10.minisql";
+    let mut store: Store<Data> = create_or_connect().await?;
 
-    // WARNING: Number of columns is 5?????
-
-    let mut store = Store::new(blob_name, 5).await.map_err(|e| e.to_io_or_panic())?;
-
-    // let store_bytes = store.get_all_bytes().await.map_err(|e| e.to_io_or_panic())?;
-    // println!("{:?}", store_bytes);
-
-    let mut buff: Vec<u8> = vec![0;1];
-    let x = store.file.read_exact(&mut buff[..]).await?;
-    println!("{:?}", buff);
-
-
-    // let entry0: Entry<u32> = Entry::new_deleted(vec![1, 2, 3, 4, 5]);
-    // let entry1: Entry<u32> = Entry::new_deleted(vec![200,200,5,6,7]);
-    // let cursor0 = store.append_entry(&entry0).await.map_err(|e| e.to_io_or_panic())?;
-    // // println!("cursor0 = {}", cursor0);
-
-    // let cursor1 = store.append_entry(&entry1).await.map_err(|e| e.to_io_or_panic())?;
-    // println!("cursor0 = {}, cursor1 = {}", cursor0, cursor1);
-
-    // let mut store = Store::connect(blob_name).await.map_err(|e| e.to_io_or_panic())?;
+    // let entry0 = read_entry(&mut store, 16).await?;
+    // let entry1 = read_entry(&mut store, 45).await?;
     // println!("{:?}", store);
+    // println!("{:?}", store.read_all_bytes().await?);
+
+    // let entry0: Entry<u32> = Entry::new(vec![99, 98, 97, 96, 95]);
+    // append_entry(&mut store, &entry0).await?;
+
+    store.read_entries(4).await.map_err(|e| e.to_io_or_panic())?;
 
-    // let x = store.entry_at::<u32>(16).await.map_err(|e| e.to_io_or_panic())?;
-    // println!("{:?}", x);
 
-    // let store_bytes = store.get_all_bytes().await.map_err(|e| e.to_io_or_panic())?;
-    // println!("{:?}", store_bytes);
 
-    // let mut store = ColumnStore::connect("blob08.minisql").await.map_err(|e| e.to_io_or_panic())?;
     // let entry2: StoreEntry<u32> = StoreEntry::new_deleted(vec![3, 2, 1]);
     // let cursor2 = store.append_entry(&entry2).await.map_err(|e| e.to_io_or_panic())?;
     // println!("cursor2 = {}", cursor2);

storage_engine/src/storage_engine.rs

@@ -1,101 +1,29 @@
-use tokio::io::{BufReader, BufWriter, AsyncReadExt, AsyncWriteExt, AsyncSeekExt, SeekFrom};
-use tokio::sync::{Mutex, RwLock};
-use tokio::fs::{File, OpenOptions};
-use tokio::fs;
+use tokio::io::{AsyncReadExt, AsyncWriteExt, AsyncSeekExt, SeekFrom};
+use tokio::fs::{File, OpenOptions, DirBuilder};
+use std::path::Path;
+use std::marker::PhantomData;
 
 use bincode;
-use bincode::de::Decoder;
-use bincode::enc::write::Writer;
-use bincode::enc::Encoder;
-use bincode::{BorrowDecode, Decode, Encode};
-use bincode::config::{BigEndian, Configuration, Fixint};
+use bincode::{Decode, Encode};
+use crate::binary_coding::{encode, decode, encode_sequence, decode_sequence};
+use tokio::fs;
+
+use crate::error::{Error, DecodeErrorKind};
 
 use std::mem::size_of;
 
+type Result<T> = std::result::Result<T, Error>;
 
-// =============Byte encoding/decoding============ 
-const BIN_CONFIG: Configuration<BigEndian, Fixint> = bincode::config::standard().with_big_endian().with_fixed_int_encoding();
+pub type Column = u64;
+pub type Cursor = u64;
 
-fn encode<T: Encode>(t: &T) -> Result<Vec<u8>, bincode::error::EncodeError> {
-    bincode::encode_to_vec(t, BIN_CONFIG)
-}
-
-fn decode<T: Decode>(bytes: &[u8]) -> Result<(T, usize), bincode::error::DecodeError> {
-    bincode::decode_from_slice(bytes, BIN_CONFIG)
-}
-
-fn encode_vector<T: Encode>(ts: &[T]) -> Result<Vec<u8>, bincode::error::EncodeError> {
-    let size: usize = ts.len();
-    let mut result = encode(&size)?;
-    for t in ts {
-        result.append(&mut encode(&t)?);
-    }
-    Ok(result)
-}
-
-fn decode_vector<T: Decode>(bytes: &[u8]) -> Result<Vec<T>, bincode::error::DecodeError> {
-    let mut offset = size_of::<usize>();
-    let result_len: usize = decode(&bytes[..offset])?.0;
-    let mut result: Vec<T> = Vec::with_capacity(result_len);
-    for _ in 0..result_len {
-        let (x, bytes_consumed) = decode::<T>(&bytes[offset..])?;
-        offset += bytes_consumed;
-        result.push(x);
-    }
-    Ok(result)
-}
-
-// We don't care about encoding the length here (since it will be used for a row with known column
-// size)
-fn encode_sequence<T: Encode>(ts: &[T]) -> Result<Vec<u8>, bincode::error::EncodeError> {
-    let mut result = vec![];
-    for t in ts {
-        result.append(&mut encode(&t)?);
-
-    }
-    Ok(result)
-}
-
-fn decode_sequence<T: Decode>(len: usize, bytes: &[u8]) -> Result<Vec<T>, bincode::error::DecodeError> {
-    let mut result: Vec<T> = Vec::with_capacity(len);
-    let mut offset = 0;
-    for _ in 0..len {
-        let (x, bytes_consumed) = decode::<T>(&bytes[offset..])?;
-        offset += bytes_consumed;
-        result.push(x);
-    }
-    Ok(result)
-}
-
-
-fn example_encoding_decoding() {
-    let xs: Vec<u32> = vec![123, 250, 256, 123, 123, 123];
-    let xs: Vec<u32> = vec![];
-    let xs: Vec<u32> = vec![123];
-    let xs: Vec<u32> = vec![123, 250];
-
-    let xs: Vec<String> = vec!["foo".to_string(), "bar".to_string()];
-
-
-    println!("original {:?}", xs);
-    let exs = encode_vector(&xs[..]).unwrap();
-    println!("encoded {:?}", exs);
-
-    // WARNING: Don't forget to specify the type here
-    // let dxs = decode_vector::<u32>(&exs[..]).unwrap();
-    let dxs = decode_vector::<String>(&exs[..]).unwrap();
-    println!("decoded {:?}", dxs);
-}
-
-// ============Column Store===============
-
-// ColumnStore
+// TODO: Consider introducing a phantom type for the data that's used in the store.
 #[derive(Debug)]
-pub struct Store {
-    column_file_name: String,
-    // TODO: This should be private
-    pub file: File,
-    header: StoreHeader
+pub struct Store<T> {
+    table_folder: String,
+    file: File,
+    header: StoreHeader,
+    data_type: PhantomData<T>,
     // meta
     //   location of rows file
     //   locations of index files
@@ -104,246 +32,322 @@ pub struct Store {
     // list
 }
 
-// These type aliases are here because they make writing decoders easier.
-type NumberOfColumns = usize;
-type DeletedCount = usize;
 #[derive(Debug)]
 pub struct StoreHeader {
-    number_of_columns: NumberOfColumns,
-    deleted_count: DeletedCount,
+    number_of_columns: usize,
+    deleted_count: usize,
+}
+impl StoreHeader {
+    const NUMBER_OF_COLUMNS_SIZE: usize = size_of::<usize>();
+    const DELETED_COUNT_SIZE: usize = size_of::<usize>();
+    const SIZE: usize = Self::NUMBER_OF_COLUMNS_SIZE + Self::DELETED_COUNT_SIZE;
+}
+
+#[derive(Debug)]
+pub struct EntryHeader {
+    is_deleted: bool,
+}
+impl EntryHeader {
+    const IS_DELETED_SIZE: usize = size_of::<bool>();
+    const HEADER_SIZE: usize = Self::IS_DELETED_SIZE;
+}
+
+#[derive(Debug)]
+pub struct EntryHeaderWithDataSize {
+    is_deleted: bool,
+    data_size: usize, // in bytes
+}
+impl EntryHeaderWithDataSize {
+    const IS_DELETED_SIZE: usize = size_of::<bool>();
+    const DATA_SIZE_SIZE: usize = size_of::<usize>();
+    const SIZE: usize = Self::IS_DELETED_SIZE + Self::DATA_SIZE_SIZE;
 }
 
 #[derive(Debug)]
 pub struct Entry<T> {
-    is_deleted: bool,
-    // file_position: FilePosition,
+    header: EntryHeader,
     data: Vec<T>,
 }
 
 #[derive(Debug)]
-pub enum Error {
-    DecodeError(DecodeErrorKind, bincode::error::DecodeError),
-    EncodeError(bincode::error::EncodeError),
-    IoError(std::io::Error),
-    InvalidStoreHeader,
+pub struct EntryDetailed<T> {
+    header: EntryHeaderWithDataSize,
+    data: Vec<T>,
 }
 
-#[derive(Debug)]
-pub enum DecodeErrorKind {
-    StoreHeaderNumberOfColumns,
-    StoreHeaderDeletedCount,
-    EntryData,
-    EntryIsDeleted,
-    EntryDataSize
+//===Store===
+pub async fn store_exists(table_folder: &str) -> Result<bool> {
+    Ok(fs::metadata(table_folder).await.is_ok())
 }
 
-// ===Errors===
-impl Error {
-    pub fn to_io_or_panic(self) -> std::io::Error {
-        use Error::*;
-        match self {
-            IoError(err) => err,
-            err => {
-                println!("{:?}", err);
-                panic!();
-            }
-        }
-    }
-}
-
-impl From<bincode::error::EncodeError> for Error {
-    fn from(err: bincode::error::EncodeError) -> Self {
-        Self::EncodeError(err)
-    }
-}
-
-impl From<std::io::Error> for Error {
-    fn from(err: std::io::Error) -> Self {
-        Self::IoError(err)
-    }
-}
-
-
-// ====Entry====
-impl <T>Entry<T> {
-    pub fn new(data: Vec<T>) -> Self {
-        Self { is_deleted: false, data }
+impl <T>Store<T> {
+    //===primitive file operations===
+    // Moves the cursor right.
+    async fn write_bytes(&mut self, bytes: &[u8]) -> Result<usize> {
+        Ok(self.file.write(bytes).await?)
     }
 
-    pub fn new_deleted(data: Vec<T>) -> Self {
-        Self { is_deleted: true, data }
+    // Moves the cursor right.
+    async fn read_bytes(&mut self, bytes: &mut [u8]) -> Result<()> {
+        self.file.read_exact(bytes).await?;
+        Ok(())
     }
 
-    // FORMAT: [HEADER, ..sequence of data]
-    //     HEADER: [Boolean (one byte), number of bytes in the data (not including the boolean)]
-    fn encode(self: &Entry<T>) -> Result<Vec<u8>, Error> 
-        where T: Encode
-    {
-        let mut result: Vec<u8> = encode(&self.is_deleted)?; // bool 1 byte
-        let mut encoded_data = encode_sequence(&self.data[..])?;
-        let encoded_data_len = encoded_data.len();
-        result.append(&mut encode(&encoded_data_len)?); // usize 8 bytes
-        println!("enc data len == {}", encoded_data_len);
-        println!("encoded_data == {:?} ", encoded_data);
-        result.append(&mut encoded_data); // data variable size
+    // Moves the cursor right.
+    async fn get_bytes(&mut self, count: usize) -> Result<Vec<u8>> {
+        let mut result: Vec<u8> = Vec::with_capacity(count);
+        self.read_bytes(&mut result).await?;
         Ok(result)
     }
 
-    // in bytes
-    pub fn header_size() -> usize {
-        size_of::<bool>() + size_of::<usize>()
+    async fn seek_to(&mut self, cursor: Cursor) -> Result<()>{
+        self.file.seek(SeekFrom::Start(cursor)).await?;
+        Ok(())
     }
 
-    // TODO: Maybe introduce an EntryHeader as a separate type?
-    pub fn decode_header(header_bytes: Vec<u8>) -> Result<(bool, usize), Error> {
-        let (is_deleted, offset) =
-            decode::<bool>(&header_bytes)
-                .map_err(|e| Error::DecodeError(DecodeErrorKind::EntryIsDeleted, e))?;
+    async fn seek_to_start(&mut self) -> Result<()> {
+        self.file.seek(SeekFrom::Start(0)).await?;
+        Ok(())
+    }
 
-        let (data_size, _) = 
-            decode::<usize>(&header_bytes[offset..])
-                .map_err(|e| Error::DecodeError(DecodeErrorKind::EntryDataSize, e))?;
-        Ok((is_deleted, data_size))
+    async fn seek_to_end(&mut self) -> Result<()> {
+        self.file.seek(SeekFrom::End(0)).await?;
+        Ok(())
+    }
+
+    async fn seek_to_start_of_data(&mut self) -> Result<()> {
+        self.seek_to(StoreHeader::SIZE as u64).await
+    }
+
+    async fn current_cursor(&mut self) -> Result<Cursor> {
+        let next_cursor: Cursor = self.file.stream_position().await?;
+        Ok(next_cursor)
+    }
+
+    // For debugging.
+    // Moves cursor to the end.
+    pub async fn read_all_bytes(&mut self) -> std::result::Result<Vec<u8>, std::io::Error>{
+        let mut bytes: Vec<u8> = vec![];
+        self.seek_to_start().await.map_err(|e| e.to_io_or_panic())?;
+        self.file.read_to_end(&mut bytes).await?;
+        Ok(bytes)
+    }
+
+    const ROWS_FILE_NAME: &'static str = "rows";
+
+    // ===Creation===
+    pub async fn new(table_folder: &str, number_of_columns: usize) -> Result<Self> {
+        let path_to_table = Path::new(table_folder);
+        let path_to_rows = path_to_table.join(Self::ROWS_FILE_NAME);
+        DirBuilder::new()
+            .create(path_to_table).await?;
+
+        let file: File =
+            OpenOptions::new()
+                .write(true)
+                .read(true)
+                .create_new(true)
+                .open(path_to_rows)
+                .await?;
+
+        let header = StoreHeader {
+            number_of_columns,
+            deleted_count: 0,
+        };
+        let encoded_header: Vec<u8> = header.encode()?;
+
+        let mut store = Self {
+            table_folder: table_folder.to_string(),
+            file,
+            header,
+            data_type: PhantomData::<T>,
+        };
+        store.write_bytes(&encoded_header).await?;
+        Ok(store)
+    }
+
+    pub async fn connect(table_folder: &str) -> Result<Self> {
+        let path_to_table = Path::new(table_folder);
+        let path_to_rows = path_to_table.join(Self::ROWS_FILE_NAME);
+
+        let mut file: File =
+            OpenOptions::new()
+                .read(true)
+                .write(true)
+                .open(path_to_rows)
+                .await?;
+
+        // Unfortunately we can't yet use store.read_bytes, since it can't be created without the
+        // header.
+        let mut header_bytes = StoreHeader::decode_buffer();
+        file.read_exact(&mut header_bytes).await?;
+        let header = StoreHeader::decode(&mut header_bytes).await?;
+
+        Ok(Self {
+            table_folder: table_folder.to_string(),
+            file,
+            header,
+            data_type: PhantomData::<T>,
+        })
+    }
+
+    // ===Append Entry===
+    // Moves cursor to the end.
+    pub async fn append_entry(&mut self, entry: &Entry<T>) -> Result<Cursor> 
+        where T: Encode
+    {
+        let encoded_entry: Vec<u8> = entry.encode()?;
+        self.seek_to_end().await?;
+        let cursor: Cursor = self.current_cursor().await?;
+        self.write_bytes(&encoded_entry).await?;
+        Ok(cursor)
+    }
+
+
+    // ===Lookup===
+    // WARNING: The cursor has to be at the start of an entry. Otherwise garbage data will be
+    // decoded as an entry.
+    pub async fn read_entry_header_at(&mut self, cursor: Cursor) -> Result<EntryHeaderWithDataSize>  {
+        self.seek_to(cursor).await?;
+        self.file.seek(SeekFrom::Start(cursor)).await?;
+
+        let mut header_bytes: Vec<u8> = vec![0; EntryHeaderWithDataSize::SIZE];
+        self.read_bytes(&mut header_bytes).await?;
+        let header = EntryHeaderWithDataSize::decode(&mut header_bytes[..])?;
+        // TODO: Get rid of the println's
+        // println!("HEADER_BYTES: {:?}", header_bytes);
+        // println!("HEADER: {:?}", header);
+
+        Ok(header)
+    }
+
+    pub async fn read_entry_data(&mut self, header: &EntryHeaderWithDataSize) -> Result<Vec<T>> {
+        let mut data_bytes: Vec<u8> = vec![0; header.data_size];
+        // TODO: Get rid of the println's
+        // println!("HEADER_BYTES: {:?}", header_bytes);
+        // println!("PREPARED_DATA_BYTES: {:?}", data_bytes);
+        self.read_bytes(&mut data_bytes).await?;
+        todo!()
+    }
+
+    pub async fn read_entry_at(&mut self, cursor: Cursor) -> Result<EntryDetailed<T>> 
+        where T: Decode
+    {
+        let header = self.read_entry_header_at(cursor).await?;
+
+        let mut data_bytes: Vec<u8> = vec![0; header.data_size];
+        // TODO: Get rid of the println's
+        // println!("PREPARED_DATA_BYTES: {:?}", data_bytes);
+        self.read_bytes(&mut data_bytes).await?;
+        // println!("DATA_BYTES: {:?}", data_bytes);
+        let entry: EntryDetailed<T> =
+            EntryDetailed::decode(header, self.header.number_of_columns, &mut data_bytes)?;
+
+        Ok(entry)
+    }
+
+    pub async fn read_entries(&mut self, n: usize) -> Result<()> 
+        where T: Decode + std::fmt::Debug
+    {
+        self.seek_to_start_of_data().await?;
+        let mut cursor: Cursor = self.current_cursor().await?;
+        for i in 0..n {
+            let entry = self.read_entry_at(cursor).await?;
+            println!("({}, {:?})", i, entry);
+            cursor = self.current_cursor().await?;
+        }
+        Ok(())
     }
 }
 
-pub type Column = u64;
-pub type Cursor = u64;
-
+// ===Store Header===
 impl StoreHeader {
-    fn encode(&self) -> Result<Vec<u8>, Error> {
+    fn encode(&self) -> Result<Vec<u8>> {
         // FORMAT: First Number of Columns, Then Deleted Count.
         let mut result = encode(&self.number_of_columns)?;
         result.append(&mut encode(&self.deleted_count)?);
         Ok(result)
     }
 
-    async fn decode(file: &mut File) -> Result<StoreHeader, Error> {
-        let number_of_columns_size = size_of::<NumberOfColumns>();
-        let deleted_count_size = size_of::<DeletedCount>();
-        let header_size: usize = number_of_columns_size + deleted_count_size;
-        let mut header_bytes: Vec<u8> = vec![0; header_size];
-        // TODO: Why do we need to have mutable reference for the file when we are reading it?
-        match file.read_exact(&mut header_bytes).await {
-            Ok(_) => {
-                let offset = 0;
-                let (number_of_columns, offset) =
-                    decode::<NumberOfColumns>(&header_bytes[offset..offset + number_of_columns_size])
-                        .map_err(|e| Error::DecodeError(DecodeErrorKind::StoreHeaderNumberOfColumns, e))?;
-                let (deleted_count, _) =
-                    decode::<DeletedCount>(&header_bytes[offset..offset + deleted_count_size])
-                        .map_err(|e| Error::DecodeError(DecodeErrorKind::StoreHeaderDeletedCount, e))?;
-                let header = StoreHeader {
-                    number_of_columns,
-                    deleted_count,
-                };
-                Ok(header)
-            },
-            Err(err) => {
-                // TODO: When err is of the kind UnexpectedEof, return InvalidStoreHeader
-                println!("ARE WE HERE?");
-                Err(Error::from(err))
-            }
-        }
-    }
-}
-
-
-impl Store {
-    // For debugging
-    pub async fn get_all_bytes(mut self) -> Result<Vec<u8>, Error>{
-        let mut bytes: Vec<u8> = vec![];
-        use std::io::Read;
-        // for byte in self.file.bytes() {
-        // }
-        self.file.read_exact(&mut bytes[..]).await?;
-        Ok(bytes)
+    fn decode_buffer() -> [u8; StoreHeader::SIZE] {
+        [0; StoreHeader::SIZE]
     }
 
-    pub async fn new(column_file_name: &str, number_of_columns: usize) -> Result<Self, Error> {
-        let mut file =
-            OpenOptions::new()
-                .write(true)
-                .read(true)
-                .create_new(true)
-                .open(column_file_name)
-                .await?;
-
+    async fn decode(result: &mut [u8]) -> Result<StoreHeader> {
+        let offset = 0;
+        let (number_of_columns, offset) =
+            decode::<usize>(&result[offset..offset + Self::NUMBER_OF_COLUMNS_SIZE])
+                .map_err(|e| Error::DecodeError(DecodeErrorKind::StoreHeaderNumberOfColumns, e))?;
+        let (deleted_count, _) =
+            decode::<usize>(&result[offset..offset + Self::DELETED_COUNT_SIZE])
+                .map_err(|e| Error::DecodeError(DecodeErrorKind::StoreHeaderDeletedCount, e))?;
         let header = StoreHeader {
             number_of_columns,
-            deleted_count: 0,
-        } ;
-        let encoded_header = header.encode()?;
-        file.write(&encoded_header).await?;
-        println!("is something being encoded? {:?}", encoded_header);
-        let store = Self {
-            column_file_name: column_file_name.to_string(),
-            file,
-            header,
+            deleted_count,
         };
-        Ok(store)
-    }
 
-    pub async fn connect(column_file_name: &str) -> Result<Self, Error> {
-        let mut file = OpenOptions::new().read(true).write(true).open(column_file_name).await?;
-
-        let header = StoreHeader::decode(&mut file).await?;
-        Ok(Self {
-            column_file_name: column_file_name.to_string(),
-            file,
-            header
-        })
-    }
-
-    pub async fn entry_at<T: Decode>(&mut self, cursor: Cursor) -> Result<Entry<T>, Error> {
-        self.file.seek(SeekFrom::Start(cursor)).await?;
-
-        // 1. read header bytes (fixed number of bytes).
-        // 2. decode header
-        // 3. read entry data bytes.
-        // 4. decode data
-        // That will tell us how much data there is.
-        let entry_header_size = Entry::<T>::header_size();
-        let mut header_bytes: Vec<u8> = vec![0; entry_header_size];
-        self.file.read_exact(&mut header_bytes).await?;
-
-        println!("cursor == {}", cursor);
-        println!("header_bytes == {:?}", header_bytes);
-
-        let (is_deleted, data_size) = Entry::<T>::decode_header(header_bytes)?;
-
-        self.file.seek(SeekFrom::Current(entry_header_size as i64)).await?;
-        let mut data_bytes: Vec<u8> = vec![0; data_size];
-
-        println!("(is_delted, data_size) = ({}, {})", is_deleted, data_size);
-        let data =
-            decode_sequence::<T>(self.header.number_of_columns, &mut data_bytes)
-                .map_err(|e| Error::DecodeError(DecodeErrorKind::EntryData, e))?;
-        Ok(Entry {
-            is_deleted,
-            data
-        })
-    }
-
-    pub async fn append_entry<T: Encode>(&mut self, entry: &Entry<T>) -> Result<Cursor, Error> {
-        // On linux when opening a file in append mode, the seek is set to 0
-        // and only updated after a write. That's why we do the cursor gymnastic at the end.
-        let encoded_entry: Vec<u8> = entry.encode()?;
-        println!("encoded_entry == {:?}", encoded_entry);
-        println!("bool size == {}", size_of::<bool>());
-        println!("usize size == {}", size_of::<usize>());
-        self.file.write(&encoded_entry).await?;
-        let next_cursor: Cursor = self.file.stream_position().await?;
-        let cursor: Cursor = next_cursor - encoded_entry.len() as u64;
-        Ok(cursor)
-    }
-
-    pub async fn iterate_all<T>(&mut self) -> Result<Cursor, Error> {
-        // Loop through the rows and print them out
-        todo!()
+        Ok(header)
     }
 }
 
+// ====Entry====
+impl EntryHeader {
+    fn encode(self: &EntryHeader) -> Result<Vec<u8>> {
+        let result: Vec<u8> = encode(&self.is_deleted)?;
+        Ok(result)
+    }
+}
+
+impl EntryHeaderWithDataSize {
+    fn decode(bytes: &mut [u8]) -> Result<Self> {
+        let (is_deleted, offset) =
+            decode::<bool>(&bytes)
+                .map_err(|e| Error::DecodeError(DecodeErrorKind::EntryIsDeleted, e))?;
+
+        let (data_size, _) = 
+            decode::<usize>(&bytes[offset..])
+                .map_err(|e| Error::DecodeError(DecodeErrorKind::EntryDataSize, e))?;
+        Ok(Self { is_deleted, data_size} )
+    }
+}
+
+impl <T>Entry<T> {
+    pub fn new(data: Vec<T>) -> Self {
+        Self { header: EntryHeader { is_deleted: false }, data }
+    }
+
+    pub fn new_deleted(data: Vec<T>) -> Self {
+        Self { header: EntryHeader { is_deleted: true}, data }
+    }
+
+    // FORMAT: [HEADER, ..sequence of data]
+    //     HEADER: [Boolean (one byte), number of bytes in the data (not including the boolean)]
+    fn encode(self: &Entry<T>) -> Result<Vec<u8>> 
+        where T: Encode
+    {
+        let mut result: Vec<u8> = self.header.encode()?;
+        let mut encoded_data = encode_sequence(&self.data[..])?;
+        let encoded_data_len: usize = encoded_data.len();
+        result.append(&mut encode(&encoded_data_len)?); // usize 8 bytes
+        result.append(&mut encoded_data); // data variable size
+        Ok(result)
+    }
+
+}
+
+impl <T>EntryDetailed<T> {
+    fn decode(header: EntryHeaderWithDataSize, number_of_columns: usize, bytes: &[u8]) -> Result<Self> 
+        where T: Decode
+    {
+        let data = decode_sequence::<T>(number_of_columns, bytes)
+            .map_err(|e| Error::DecodeError(DecodeErrorKind::EntryData, e))?;
+        Ok(EntryDetailed { header, data })
+    }
+}
+
+
+
+
 // impl StorageEngine for ColumnStore {
 //     async fn append(&mut self, id: Index, entry: Row<T>) -> Result<???, Error>